A gas turbine engine typically includes a plurality of fuel injectors for supplying fuel to a combustor of the engine. The fuel is introduced at the upstream end of the combustor in a highly atomized spray from a fuel nozzle assembly of each fuel injector. Compressed air flows around the fuel nozzle assembly and mixes with the fuel to form a fuel-air mixture, which is then combusted within a combustion zone of the combustor.
Due to a wide range of combustor operating conditions and corresponding required fuel flows, many fuel injectors include a main nozzle and one or more pilot nozzles. For example, fuel injectors are known that include both a primary pilot nozzle and a secondary pilot nozzle. Typically, the pilot nozzles are used during start-up, with both the pilot and main nozzles being used during higher power operation. For example, the flow to the main nozzles may be reduced or cut-off during start-up and lower power operation. Such fuel injectors are typically more efficient and cleaner-burning than single nozzle fuel injectors, as the fuel flow can be more accurately controlled and the fuel spray more accurately directed for the particular combustor requirements.
During certain operating events, it is often necessary to supply an enriched fuel flow to one or more of the fuel injectors to satisfy the operational requirements of the gas turbine engine. For example, to relight an engine following a high-power fuel cut (HPFC), conventional fuel control systems are configured to direct an enriched fuel flow through the primary pilot nozzle(s) of a small number of the fuel injectors. Unfortunately, primary pilot nozzles are typically configured to operate at a relatively low fuel flow number so as to provide the atomization required for low speed starts. As a result, an extremely large pressure drop is often necessary to inject the fuel flow required for an HPFC relight event through the primary pilot nozzles. Accordingly, engine designers must currently select between increasing the size of the fuel pump to provide the increased fuel pressure needed for such events (thereby, significantly increasing the overall weight of the system) or modifying the primary pilot nozzles to operate at higher fuel flow numbers (which negatively impacts the atomization for low-speed starting and operation near idle speed).
Accordingly, an improved fuel supply system that allows a portion of the fuel that would otherwise be supplied to a primary pilot nozzle to be diverted to another nozzle of the fuel injector so as to reduce the required pressure (and thus, the pump size) needed for fuel enrichment during a HPFC relight event or during any other suitable event would be welcomed in the technology.